Authorities seized equipment from the office of a Manhattan psychiatrist yesterday – after one of his patients wound up brain dead following a session, cops said.

Leah Grove, 38, is in intensive care at Bellevue Hospital, where she was taken April 19 after something “went wrong during carbon-dioxide therapy” at Dr. James Watt’s office, police said.

They said Watt was treating the Queens woman for depression with a combination of gases, including carbon dioxide, and was unable to rouse her during the procedure.

Police and prosecutors searched Watt’s office on East 46th Street and removed the equipment to determine whether there was any criminal liability.

But investigators said a preliminary examination showed the equipment was functioning properly, and it was unlikely charges would be filed in what may have been a tragic accident.

Two of Grove’s relatives keeping a vigil at her bedside yesterday would say only that they don’t know what happened.

Dr. Michael Blumenfield, a professor of psychiatry at New York Medical College and chair of the American Psychiatric Association’s joint commission on public affairs, said he does not believe carbon-dioxide therapy is an approved method for treating psychiatric disorders.

“On the surface, it sounds tricky,” he said, noting carbon dioxide’s suffocating effects. “I would be very leery of anything that compromised someone’s breathing.”

In the 1920s, carbon-dioxide therapy was thought to stimulate the brain. It was used in the 1940s and 1950s to trigger near-death experiences.